Currently available receiver media for digital offset printing presses consist of a variety of papers and films having a clay coating or clay base. The papers have a very low gloss, with only the film-based receivers exhibiting glossy surfaces.
In a digital offset printing press, the toner "link" is not absorbed into the substrate but rather resides on the surface of the media. The problem of adhesion and transfer at this toner-media interface, especially on a high gloss surface, requires that the media have a special surface treatment to promote total toner transfer and adhesion to the surface.
One type of surface treatment of paper known in the prior art does not produce a distinct layer on the paper, but rather causes the surface to become basic or alkaline. Such a process is not applicable to glossy films or resin-coated papers because it would reduce gloss, make the surface very tacky to the touch, degrade ink transfer and adhesion, and cause paper feeding and paper stacking problems resulting from the tacky surface.
PCT International Application WO 96/06384 discloses a printing method to form an image of colored toner polymer particles on a paper substrate whose surface has been treated with a compound having a basic functionality, preferably a polymeric imine. The method is purported to improve image adhesion on many but not all of the papers tested.
European Patent Application EP 0 637 603 Al discloses a polymeric film substrate coated with a polyamido-polyethyleneimine. Although the primary purpose of the applied coating is to render the coated film receptive to direct extrusion overcoating with other polymers, improved ink adhesion is also recited as an object.
UK Patent Application GB 2 212 741 A discloses a polyolefin film coated with an aqueous solution of a modified polyethylenimine compound. The coated film is intended for use as a receiver for UV-curable inks.
There is a continuing need for a receiver sheet for images from digital offset printing presses that has a glossy surface with excellent toner transfer and adhesion properties. The present invention meets this need.